Camellia sinensis (tea) seeds have been identified as potential sources of nutraceutical compounds. In this study, caffeine and theaflavanoside IV were annotated as the most abundant phytochemicals in the seed shells of C. sinensis. Both compound displayed potent inhibitions against protein tyrosine phosphatase 1B (PTP1B) with IC50 values of 37.9 ± 3.5 and 8.7 ± 1.1 µM, respectively. In the kinetic study, caffeine inhibited PTP1B with mixed type I mode, which prefers to bind to free enzyme. Theaflavanoside IV showed competitive and reversible simple slow-binding inhibition [k3 = 0.1 µM-1·min-1, k4 = 0.002 min-1, Kiapp = 0.0002 µM]. This is the first report on PTP1B-inhibitory activity of these compounds and their action mechanisms. These results suggest their potential in the development of antidiabetic agents.
Keywords: Camellia sinensis seed shell; caffeine; competitive inhibition; protein tyrosine phosphatase 1B; slow binding; theaflavanoside IV.